The basic mechanical structure of the Stoner FOW is used by way of example to illustrate the inventive concepts disclosed herein, which are representative of the applicability of these inventive concepts to other firearms systems and firearms platforms, but such inventive concepts are not to be taken to be limited to the Stoner FOW.
FIG. 1 shows an exploded view of a conventional AR-15, which serves as an example of a firearm to which aspects of the inventive improvements disclosed herein may be applied. FIG. 1 shows, among other elements, a buttstock 12, a lower receiver 14, a handle 16, a magazine well 18, a magazine 20, a trigger 22, a barrel 24, a bolt carrier 26, a bolt 28, a firing pin 30, a charging handle 32, an upper receiver 34, a gas tube 36, a bolt catch 38, a sight 40, gas rings 42, a magazine catch 44, and a magazine release button 46.
During operation of a direct impingent type firearm, such as the AR-15 shown in FIG. 1, gas travels down the gas tube 36 located above the barrel 24. The gas tube 36 is operatively connected to a bolt carrier key 48, allowing the gas from the gas tube 36 to pass into the bolt carrier 26. The bolt 28 and bolt carrier 26 together act as a piston (bolt 28) and cylinder (bolt cavity or recess within carrier body), which moves as the bolt carrier 26 cavity is filled with gas which pushes the bolt and carrier body apart via expansion of gasses. The bolt 28 is incapable of rearward movement when it is locked to barrel extension 50. It unlocks from the extension via rotation of the bolt controlled by the cam path or slot and the movement of the cam pin 52 within the cam path which controls rotational movement or turning of the bolt. This impacts both the movement out of battery (“unlocking”) and movement into battery (“locking”). Therefore, when the bolt carrier 26 is filled with gas, the bolt carrier 26 is forced backward by interaction of the expanding gasses creating movement between the bolt 28 and bolt recess within the carrier body—which are kept together by the cam pin moving within the cam path, toward the buttstock 12.
FIG. 2 shows the conventional bolt 28 in more detail, depicting the main body 80, rectangular lugs 68 disposed at the front end of the bolt 28 (i.e., the end closer to the barrel 24 when assembled in a firearm), ribs 78 adjacent to the lugs 68, a tail portion 70 disposed at the rear end of the bolt 28 (i.e., the end farther from the barrel 24 when assembled), a gas ring 42 adjacent to the tail portion 70, a decreased diameter portion 72 adjacent to the gas ring 42, a through hole 74 adjacent to the decreased diameter portion 72, a wear ring 76 disposed between the through hole 74 and the lugs 66.
A cam pin 52, riding in a slot on the bolt carrier 26, forces the bolt 28 to turn and unlock from the barrel extension 50. Once the bolt 28 is unlocked, the bolt 28 moves rearward along with the bolt carrier 26. The rearward motion of the bolt 28 extracts an empty cartridge case from the chamber, and a spring-loaded ejector 54 forces the cartridge out the ejection port 56. Behind the bolt carrier is an in-line buffer 58 with an action or buffer spring 60 that pushes the bolt carrier 26 back toward the chamber. A groove of the upper receiver guides the cam pin 52 and prevents it and the bolt 28 from rotating into a closed position. The locking lugs of the bolt 28 then push a fresh round from the magazine as the bolt moves forward. As the bolt's locking lugs move past the barrel extension, the cam pin 52 twists into a pocket milled into the upper receiver, following the groove cut into the carrier, and forces the bolt to twist and “lock” into battery the barrel extension.
While the Stoner FOW has been known in the public for well over 50 years (see, e.g., U.S. Pat. No. 2,951,424, titled “Gas Operated Bolt and Carrier System,” published Sep. 6, 1960, incorporated by reference herein in its entirety), and has been oft-modified in such time, there remains room for further improvements.